Presently known surveillance means include detectors in communication with visual or audio output devices for delivering signals from said detectors to alert personnel responsible for taking action under appropriate circumstances, or which are in direct communication with protection devices which are brought into operation automatically, for example sprinklers for sprinkling water or some other product for fire-fighting purposes, or devices for ejecting a gas to hinder the destructive acts of vandals.
Such detectors may be thermal detectors which respond to temperature, electronic detectors which respond to infrared radiation, to ultrasonic waves, or to radar emissions for detecting displacement within a monitored volume. Detectors are sometimes accompanied by means for instantly displaying the place under surveillance, using a video camera or micro-camera connected to a monitor screen.
Regardless of the effective range of any such surveillance device, and regardless of its angle of observation, the area or volume over which any one device is effective is always limited. This remains true even when such devices are rotatable about an axis in order to increase their effective range by a rotating or scanning action.
Such devices can be made effective over a larger area by multiplying the number of devices, thereby increasing expense, even if individual devices are cheap, which is not always the case.
An object of the present invention is thus to increase the field of observation of a given surveillance device in a manner which may be practically unlimited.